1. Field of the Invention
The invention relates to a projector and a method for projecting a light beam with the projector. More particularly, the invention relates to a projector and a method for adjusting a light beam of the projector.
2. Description of the Prior Art
A conventional projector has a phosphor wheel, which comprises a plurality of phosphor coating areas. Each of the phosphor coating areas is used to radiate phosphorescence of a specific color when the phosphor wheel is illuminated by a light beam from a light source of the projector. For example, a phosphor wheel has three phosphor coating areas for radiating red, green and blue phosphorescence respectively. When the projector is turned on, the phosphor rotates so that the phosphor coating areas would be sequentially and periodically illuminated by the light beam of the light source so as to radiate phosphorescence of different colors. However, since the intensity of the light beam of the light source may not be constant, and the phosphor may not be uniformly coated on the surface of the phosphor wheel, the white balance of the projector may be incorrect.
Please refer to FIG. 1. FIG. 1 shows that the relationship between the intensity of the light beam of the light source and the brightness of the phosphor wheel is not linear. Accordingly, the brightness of the phosphor wheel cannot be linearly controlled by adjusting the intensity of the light source, and the difficulty of controlling the brightness of the phosphor wheel is increased.
Please refer to FIG. 2. FIG. 2 is a diagram showing the relationship between the brightness of the phosphor wheel and the illuminated area of the phosphor wheel while all areas of the phosphor wheel are illuminated by the light beam with the same intensity. Since the phosphor on the phosphor wheel is not uniformly coated on the surface of the phosphor wheel, the brightness of the phosphor wheel is not constant. Therefore, the quality of the image of the projector is deteriorated. For example, the white balance of the projected images cannot be optimized.
Please refer to FIG. 3. FIG. 3 is a diagram showing that the real brightness of the projector would decay along with time. After the projector is turned on, since temperature of the phosphor wheel and the light source increase, both the efficiency of the phosphor wheel for generating phosphorescence and the efficiency of the light source for generating the light beam would decrease. This would result in poor white balance of the projector.